"I'm very happy that I could come and meet with my friends on the eve of my birthday," Grass, who won the Nobel Prize for literature in 1999, was quoted as saying by the PAP news agency.

Grass was to meet with former Polish President Lech Walesa, also a Nobel laureate, for a discussion of German-Polish relations - a topic long important to Grass, author of "The Tin Drum," "Cat and Mouse," "Dog Years" and other works.

A year ago, Grass revealed in his memoir, "Skinning the Onion," that as a teenager, he had served in the Waffen-SS, the combat arm of Adolf Hitler's notorious paramilitary organization.

The confession struck a nerve in Poland, which Nazi Germany invaded and then subjected to a brutal occupation under which some 6 million Poles - roughly half of them Jews - perished.

The late revelation raised calls from politicians - including Walesa - for the author to be stripped of his honorary citizenship in Gdansk.

In response, Grass wrote a letter to the city's mayor, Pawel Adamowicz, saying that only in his old age did he find the "right formula" to talk about serving in the SS. The mayor accepted Grass' explanation, and the author kept his honorary citizenship.

"I experienced an example of tolerance in my exchange of letters with mayor Adamowicz and Lech Walesa," PAP quoted Grass as saying. "In those difficult days, it was a great help for me."

Grass served in the 10th SS Panzer Division, which fought Soviet troops in eastern Germany near the end of the war. He was wounded and then taken prisoner by U.S. forces.

The author has long been respected as a moral authority in Poland and elsewhere. Poland enthusiastically welcomed the fact that Grass for decades urged his fellow Germans to confront their nation's past crimes and promoted reconciliation between the neighboring nations.